The present invention relates generally to elevator systems and, in particular, to equipment for ascertaining the absolute position of a rail-guided elevator car in an elevator shaft.
Such position transmitting equipment is known. In elevator installations, these are used for the purpose of determining the absolute position of an elevator car and deriving therefrom data signals for control of the elevator installation. The position information is applied in a coded form in fixed location along the entire travel path of the elevator car and is read off in the coded form by means of a code reading device and processed in evaluating equipment to be comprehensible to the control.
For example, equipment is known from German Utility Model G 92 10 996.9 in which a magnetic strip functioning as a code carrier is laterally fastened to a car guide rail. The magnetic strip contains, in the displacement direction of the elevator car, a length coding and coded data about stopping points or the like. A magnet head fastened to the elevator car and movable in common therewith relative to the magnetic strip in the reading direction of the coding reads off the coded data and passes on the data for evaluation.
Disadvantages of the known equipment consist in the previously usual application of the magnetic strip at or on the car guide rail and also in the construction of the magnetic strip itself. The magnetic strip has to be mounted at the guide rail in positionally exact manner and without overstretching in order to avoid misalignment of the coding with the corresponding position and inaccuracies, which result therefrom, for the positioning of the elevator car. Moreover, unequal thermal expansions of the magnetic strip relative to the car guide rail occur, which has the consequence of a displacement of the coding relative to the guide rail. In addition, the exposed position of the magnetic strip laterally at the guide rail involves the risk of mechanical damage to the magnetic strip by parts moved in the shaft, such as, for example, the magnet head in the case of horizontal movements of the elevator car. The known magnetic strip clogs with lubricating oil and dust particles swirled up in the shaft, which impairs reading of the coding.